This invention relates to a plasma-addressed colour display device comprising: a layer of electro-optical material sandwiched between elongated data electrodes and plasma channels to obtain a matrix structure of pixelelements, and colour filters being associated with the pixelelements for obtaining groups of adjacent pixelelements representing different colours enabling display of a colour picture.
The publication xe2x80x9cA 16 Inch Full Colour Plasma-addressed Active-Matrix LCDxe2x80x9d, Digest of Technical Papers, 1993 SID International Symposium, Soc. for Info. Display pp. 883-886 by Buzak et al., discloses a plasma-addressed liquid crystal display, commonly referred to as xe2x80x9cPALCxe2x80x9d display device, more specifically a colour PALC display device. The known PALC display device comprises: a first substrate on which parallel transparent column electrodes are deposited, a second substrate which has parallel sealed plasma channels corresponding to rows of the display, and a liquid crystal material (LC-material) sandwiched between the substrates. Each of the plasma channels of the second substrate is filled with a low pressure ionizable gas, such as helium, and contains spaced cathode and anode electrodes along the channel for ionizing the gas to create a conductive plasma. The channels are closed off by a thin transparent dielectric sheet. Each of the plasma channels crosses all of the column electrodes to form a matrix of overlapping regions. The overlapping regions correspond to pixelelements of the electro-optical material.
The operation of the PALC display device is elucidated below. The plasma channel acts as a row switch capable of selectively addressing a row of liquid crystal pixel elements (LC-pixels). Successive lines of data signals representing an image to be displayed are sampled at column positions and the sampled data voltages are respectively applied to the column electrodes. All but one of the row plasma channels are in the deionized or non-conducting state. The plasma of the one ionized selected plasma channel is conducting and, in effect, establishes a reference potential on the adjacent side of a row of LC-pixels, causing each LC-pixel to charge to the difference of the reference potential and the column potential. Then, the ionized channel is turned off for isolating the LC-pixel charge and storing the data voltage for a frame period. When the next row of data appears on the column electrodes, only the succeeding plasma channel row is ionized to store the data voltages in the succeeding row of LC-pixels, and so on. As is well known, the attenuation of each LC-pixel to backlight or incident light is a function of the stored voltage across the pixel.
The plasma channels can be activated successively, for example by applying successively a large voltage pulse to the anode electrodes, whereby each of the cathode electrodes is coupled to a reference voltage.
To obtain a colour display, colour filters are provided representing three primary colours. The colour filters each are spatially aligned with a corresponding one of the data columns. Each intersection of one plasma channel extending in the row direction with three data columns (one for red, green, and blue) extending in the column direction defines a full colour pixel. In this way groups of three adjacent LC pixels are obtained of which each pixel is associated with another of the primary colours.
The known display device has as a drawback that many data drivers are needed to supply the data signals to the data columns.
It is an object of the invention to provide a display device of which a total number of drivers is decreased.
An aspect of the invention is characterized in that the display device is adapted to comprise groups of pixelelements each being constituted with a common data electrode cooperating with a group of plasma channels, the colour filters being aligned with the plasma channels. The groups of pixelelements form a full colour pixelelement. A group of pixelelements is constituted out of one data electrode extending in the column direction and a group of plasma channels extending in the row direction instead of one plasma channel extending in the row direction and a group of data electrodes each extending in the column direction. Different colour filters are aligned with each of the plasma channels of the group. So, the colour filters now extend in the row direction instead of the column direction. The number of plasma channels and colour filters in a group may be three such that each of the colour filters represent a primary colour. In this case, the number of data electrodes and thus the number data drivers connected thereto reduces by a factor three, and the number of plasma channels increases with a factor three. The total number of drivers decreases if in the known PALC display the number of colour pixelelements in a row (so, the number of data electrodes divided by three) is larger than the number of rows (which are the plasma channels). This is usually the case as in most display panels the number of pixelelements in a row is larger than the number of rows. As an example, suppose a known PALC display device with an 3:4 aspect ratio has 600 rows (plasma channels) and 3*800 columns (data electrodes). The total number of drivers is not less than 3000, viz. 600 pulse drivers connected to the anode electrodes (all the cathode electrodes may be interconnected to receive the reference voltage, as will be further explained below) and 2400 data drivers connected to the data electrodes. The PALC display device according to the invention comprises 800 data columns and 3*600 plasma channels. The total number of drivers is only 2600, viz. 3*600 for the anode and cathode electrodes and 800 for the data electrodes.
In accordance with an embodiment of the invention an advantageous way of driving the plasma-addressed colour display device will be described. In the known PALC display a video signal has to be processed into data signals representing three primary colours (usually: red, green, blue). The data signals are supplied to corresponding data electrodes via a data driver circuit. The data driver circuit supplies the data signals associated with the different colours in parallel to all column electrodes. The plasma channels are selected one by one via a plasma driver circuit and thus a row of pixels corresponding to the selected plasma channel will be charged. A common plasma channel cooperates with a group of three data electrodes to obtain a full colour pixel. In contrast with the known PALC display, the plasma driver circuit according to the invention is adapted to select the plasma channels in a group one by one. The data driver circuit according to the invention is adapted to supply the data signals belonging to the group of colours one by one to the common data electrode such that the data of a specific colour is presented to the activated plasma channel associated to a colour filter corresponding to that colour.
In accordance with another embodiment of invention, a further reduction of the total number of drivers is reached.
EP-B-0,325,387 shows that the number of drivers needed to drive a PALC display panel decreases by taking together in groups both the anode and the cathode electrodes. In EP-B-0,325,387 two possibilities are disclosed to select the plasma channels 30 one by one. The first possibility shows that one electrode of each plasma channel is connected to a reference potential. So, all these electrodes can be interconnected to receive the reference potential. The remaining electrode of each plasma channel is connected to a pulse driver supplying a pulse signal. The plasma channels are selected one by one by supplying one pulse signal with a voltage pulse which has a value with respect to the reference voltage that is large enough to ionize the plasma, while all other pulse signals supply a voltage which has a value with respect to the reference voltage that is too low to ionize the plasma. Assuming a PALC display device with N rows of pixels, N pulse drivers are needed to drive the supply the pulse signals to the anodes, and N+1 connections are needed to supply the N pulse signals and the one reference signal to the panel if the all cathodes are interconnected on the PALC display panel. The second possibility shows that the number of drivers needed to drive a PALC display panel decreases by taking together in groups both the anode and the cathode electrodes. The groups are chosen such that each of the anode groups includes no more than one electrode of each of the cathode groups, and in the same way, each of the cathode groups includes no more than one electrode of each of the anode groups. The adjacent cathode-anode electrode pairs are each located in one channel, and the channels whose electrodes form any one of a first group thus include no more than one electrode of any one of the second group. Assuming again a PALC display device with N rows of pixels, both the cathode and anode electrodes are taken together in groups of Nxc2xd lines, with one pulse driver per group. This leads to 2Nxc2xd instead of N pulse drivers, and if the connections in each of the groups are made on the PALC display panel to 2Nxc2xd instead of N+1 connections.
Although this way of grouping the anode and cathode electrodes is very efficient a lot of other possibilities exist to group the anode and cathode electrodes whereby the demands formulated above are satisfied. Then still the number of pulse drivers decreases, but to a lesser extent. It may be advantageous to group less than the maximal allowable Nxc2xd electrodes to lower the capacitive load of the pulse driver connected to such a group of electrodes.
As for the ignition of the plasma it is only important to supply a large enough voltage difference between the anode and cathode electrodes it is possible to interchange the position of the anode and cathode electrodes. Therefor these electrodes are also referred to as first and second electrodes.
As an example, suppose a PALC display having the known structure has 1200 rows (plasma channels) and 3*1600 columns (data electrodes, 1600 for each colour). The total number of drivers needed to drive the PALC display panel is not less than about 4870, viz. 2*1200xc2xd for the anode and cathode groups and 4800 for the data electrodes. A corresponding PALC display has 3*1200 plasma channels and 1600 data electrodes. The total number of connections is only about 1720, viz. 2*(3*1200)xc2xd for the anode and cathode groups and 1600 for the data electrodes.
As an other example, suppose a PALC display having the known structure has 600 rows (plasma channels) and 3*400 columns (data electrodes, 400 for each colour). The total number of drivers needed is not less than about 1250, viz. 2*600xc2xd for the anode and cathode groups and 1200 for the data electrodes. A corresponding PALC display has 3*600 plasma channels and 400 data electrodes. The total number of drivers needed is only about 486, viz. 2*(3*600)xc2xd for the anode and cathode groups and 400 for the data electrodes. So, even if a PALC display panel with a known structure has a number of colour pixels in a row (400 in the above example) not larger than the number of rows (600 in the above sample) the total number of drivers of a PALC display decreases. The actual amount of decrease of the number of drivers is also dependent on the way the anode and cathode electrodes are grouped. The decrease will be less if less than the maximal allowable Nxc2xd electrodes are grouped.
Besides lowering the number of data drivers, also the number of data electrodes decreases and thus the spacing between the connections to the data electrodes becomes larger which is more economical and more reliable. A negative consequence of the invention is that the number of plasma channels increases a factor three, and the time available for igniting the plasma channels and the time available to charge the pixels decreases by a factor three. But, the advantages reached by the decreased number of data electrodes outweigh these disadvantages.
The invention may offer even a more substantial decrease in the total number of connections for the new displays with an aspect ratio of 16:9 in which the number of pixels in a row is likely to be even much more larger than the number of rows.
These and other aspects of the invention will be described and elucidated with reference to the accompanying drawings.